1. Field of the Invention
The present invention relates to a method for compensating gear backlash of a geared motor, the geared motor being operated in particular in an electrophotographic printing machine in order to bring about the alignment of a print medium web. An apparatus for carrying out this method is likewise provided.
2. Description of the Related Art
From U.S. Pat. No. 4,061,222, an apparatus is known that detects the edge of a band or belt and continuously adjusts the edge to a particular position via a tiltable roller over which the belt runs. Here, a sensor acquires the edge of the band or belt, and the sensor output is used to control a geared motor that correspondingly pivots the tiltable roller. A compensation of a gear backlash of the geared motor is not known from this reference.
From U.S. Pat. No. 4,174,171, a mechanical solution is known for holding a belt or band in a particular position. Here a roller over which the belt runs is held by a support that is in turn fastened to a steering post that can rotate freely. As soon as the belt has moved laterally out of the target position, a corresponding force is exerted on the steering post, so that this steering post is rotated together with the support and the roller in such a way that the belt moves back into the predetermined path.
From U.S. Pat. No. 5,717,984, a system for guiding and controlling an electrophotographic belt or band is known that includes a guide roller and a drive motor that acts on the guide control roller. A similar system, with a somewhat different design, is known from European Patent Document EP-A2-608 124.
From Published International Patent Application WO-A-99/08374, a high-precision driveable motor system is known.
From U.S. Pat. No. 5,248,027, a method is known that uses two markings on a belt or band to control the position of the belt; these two markings are acquired by a sensor and a control system drives a step motor in such a way that a guide roller around which the belt runs is pivoted. In this method, the idling, or the play, of the step motor is taken into account and is used by the control system in its calculations. The way in which this idling is determined is not addressed and also not described in this reference.
Finally, from European Patent Document EP-A1-0 699 968, an apparatus for controlling a web is known that operates using a tiltable web guide roller, whereby a device is provided for compensating an idling of the tilting device. The position of the web is also determined via sensors that acquire the edge of the web. The response characteristic of the tilting device is determined in such a way that tilting takes place first in one direction, and subsequently the device is tilted back in the opposite direction in many small steps, in order to acquire the position of the web by means of the output of the sensors, and from this to project the idling.
In the case of European Patent Document EP-A1-0 699 968, any play that may exist in the tilting device as a whole is calculated, and an attempt is made to compensate this calculated overall play. A targeted elimination of a gear backlash in a geared motor is not addressed there.
From Japanese Patent Document JP-A-4085065, a method is known for determining and compensating the play in a geared motor with reversible operation that is used in a printer. For this purpose, the motor is brought into a first state in a first direction of rotation, and is subsequently rotated in the opposite direction. Here, at the point of reversal the pulse difference of the step motor is acquired, which indicates the play of the motor and is used for its compensation in the reverse operation.
From Japanese Patent Document JP-A-63274574, a drive control system is known for a carriage, operated in reverse operation with a step motor, in a printer, in which at the point of reversal a photocell sensor is used to determine the time that passes, due to the play of the step motor, from the driving of the step motor until the carriage passes by the sensor. In order to compensate the play, the controlling of a print head is correspondingly retarded. However, such a system is relatively unsuitable for electrophotographic devices, because toner dust can settle on the light-conducting elements of the sensor, which can result in functional disturbances.
From Published International Patent Application WO-A-99/08374, a method is known for determining a gear backlash in which a plurality of Hall sensors and a torque sensor are used to detect angular positions and torque relationships between a rotary motor and an output shaft. The measurement results that are thereby achieved can however contain errors, because it cannot always be ensured that the values of the Hall sensors are detected simultaneously with the values of the torque sensor.